Scientists have embarked on a groundbreaking study that highlights the advantages of intermittent fasting. Skipping meals from 5 p.m. to 9 a.m. the next day (known as early fasting) is particularly effective for enhancing blood sugar control and decreasing abdominal subcutaneous fat, which is the fat located just beneath the skin.
Researchers from the University of Granada (UGR), the Public University of Navarra (UPNA), and CIBER have demonstrated that intermittent fasting—limiting the hours during which food is consumed and extending fasting periods each day—serves as an effective approach for weight loss and improves heart health for individuals with obesity.
Their findings, published in the journal Nature Medicine, indicate that consuming the last meal before 5 p.m. and skipping dinner is a secure and beneficial method for cutting down on subcutaneous abdominal fat, especially following indulgent times like the Christmas season.
In Spain, the rates of overweight and obesity are alarming, with about 70% of men and 50% of women affected. This condition is linked to various metabolic diseases, including type 2 diabetes, and significantly raises the risk of cardiovascular illnesses, high blood pressure, and certain cancers. This growing issue negatively affects people’s quality of life and poses a considerable challenge for public health systems. Researchers are striving to develop effective and straightforward strategies to combat what is now recognized as a disease.
While calorie-restricted diets can aid in weight loss and enhance cardiovascular health, they are often hard to sustain long-term. Consequently, many individuals end up abandoning the treatment and regaining their lost weight, sometimes even gaining additional weight.
In light of the difficulties associated with sticking to traditional calorie restriction, new dietary methods are being explored. One such method is intermittent fasting, which involves alternating between eating and fasting periods that can last for hours or even days. A popular form of intermittent fasting that has emerged recently is one where the eating window is minimized to 6-8 hours each day, extending fasting to 16-18 hours. This method, known as time-restricted eating, contrasts with the typical Spanish eating habits of having breakfast around 7-8 a.m. and dinner at around 9-10 p.m., which usually allows for a 12-14 hour eating window. By shortening this eating window to 6-8 hours, individuals can maintain a daily rhythm that can help stabilize their bodily biological clocks. Irregular eating or eating late at night can disrupt these rhythms, potentially increasing the likelihood of obesity, heart diseases, and type 2 diabetes.
The research group PROFITH CTS-977 from the Department of Physical Education and Sports at the Faculty of Sports Sciences and the Sport and Health University Research Institute (iMUDS), led by Dr. Jonatan Ruiz, collaborated with ibs.Granada, the University Hospital ClÃnico San Cecilio, and the University Hospital Virgen de las Nieves in Granada. They also worked with Dr. Idoia Labayen from the Public University of Navarra and CIBER on Obesity (CIBEROBN), as well as CIBER on Frailty and Healthy Ageing (CIBERFES), to investigate the impacts of a 12-week intervention that employed three different fasting strategies: early fasting (eating approximately from 9:00 a.m. to 5:00 p.m.), late fasting (about 2:00 p.m. to 10:00 p.m.), and self-selected fasting where participants could choose their eating times, which generally fell between noon and 8:00 p.m.
Study with 197 participants
All participants in the study also underwent standard treatment, which included an education program focusing on the Mediterranean diet and healthy lifestyle choices. This randomized, controlled, multicenter trial—one of the largest conducted to date—took place in Granada and Pamplona, involving 197 individuals (50% women) aged 30-60. Participants were randomly divided into four groups: usual treatment (49 participants), early fasting (49 participants), late fasting (52 participants), and self-selected fasting (47 participants).
This investigation formed part of the doctoral research of Manuel Dote-Montero, who currently holds a postdoctoral position at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) in the U.S. Manuel Dote-Montero, together with Antonio Clavero Jimeno, a predoctoral researcher at the UGR, and Elisa Merchán RamÃrez, also a postdoctoral researcher at the UGR, led this study in Granada. They noted that it remains uncertain whether the timing of the eating window—early, late, or self-selected—produces distinct effects on weight loss, visceral fat, which surrounds organs in the abdomen, or overall cardiovascular health among those who are overweight or obese.
The study’s results, published in the journal Nature Medicine, indicate that intermittent fasting did not provide additional benefits over the nutrition education program regarding reductions in visceral fat. However, participants in the fasting groups achieved greater weight loss, averaging 3-4 kg, compared to the usual treatment group that maintained a minimum 12-hour eating window. Importantly, those in the early fasting group experienced a more significant reduction in abdominal subcutaneous fat.
The research also included assessments of fasting and 24-hour glucose levels using continuous glucose monitors, which participants wore for 14 days before and after the intervention. Results revealed that the early fasting group made substantial improvements in fasting glucose levels compared to the other groups.
Regulating glucose
These findings suggest that early fasting might particularly aid in optimizing glucose regulation, potentially helping to prevent diabetes and enhance metabolic health. By avoiding nighttime eating, the body has more time to digest and process nutrients, which promotes better blood glucose regulation and lowers the risk of developing metabolic issues, according to Dr. Labayen, the lead investigator of the study in Pamplona and a member of CIBEROBN alongside Dr. Jonatan Ruiz and Dr. Manuel Muñoz (CIBERFES).
The researchers emphasize that all fasting groups demonstrated high adherence rates, and no severe adverse events were reported. Intermittent fasting emerges as a safe and promising approach for weight management and improving cardiovascular health in those who are overweight or obese. This information could be vital in enhancing the effectiveness of nutritional interventions for these populations.
